Answer:
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.
I can be cracked, I can be made. I can be told, I can be played.
It's anything but amusing when this body part gets hit.
My first is equality; my second is inferiority; my whole is superiority.
What goes in, but never through? I've got some and so do you. We might lend one, or even two, but only if our trust is true.
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?